In order to automatically transfer various liquid such as a reagent, sample, specimen and the like set to an apparatus to an optional position, a dispensing robot is commonly used. The dispensing robot is a unit that makes the inside of a specific range of the apparatus drive two-dimensionally or three-dimensionally, and automatically executes aspiration and discharge of the liquid by a nozzle, tip and the like (hereinafter referred to as “nozzle”) attached at the distal end thereof. The dispensing robot is used in various apparatuses such as various automatic analyzers and the like.
In various automatic analyzers and the like, liquid to be transferred (hereinafter referred to as “reagent”) is expensive in many cases. Therefore, it is necessary to minimize the use amount of a reagent required for analysis. Also, in a case of medical equipment, when transfer of liquid fails due to some cause, it is necessary to display an error so as not to lead to an erroneous diagnosis. Accordingly, a method is commonly employed in which the liquid level is detected, an amount of attachment of a nozzle to a reagent is reduced, and the use amount of the reagent is minimized. With respect to detection of the liquid level, a capacitance method in which the nozzle is made an electrode is commonly employed. By employing this method, even when the number of the container containing the reagent increases, the liquid level can be detected for all containers by one liquid level detecting function. In detecting the liquid level by the capacitance method, because the nozzle is made an electrode, it is necessary to avoid that the nozzle contacts components other than the reagent. The reason is that, when the nozzle contacts a component other than the reagent, the component contacted may be erroneously detected as the liquid level.
On the other hand, in various automatic analyzers and the like, a reagent may occasionally be required to be set to an apparatus for a long time. When the reagent is set to the apparatus for a long time, evaporation of the reagent, deterioration of the chemical components and the like are inevitable. However, the more the use amount of the reagent is reduced, the more the effect of evaporation of the reagent and deterioration of the chemical components increases. Thus, reliability of the analysis result may be damaged. In order to prevent evaporation of the reagent and deterioration of the chemical components, the air must be blocked in addition to a method of cooling the reagent.
In order to achieve both of the two functions, the reagent must be blocked against the air as much as possible while the nozzle does not contact other than the reagent. Required degree of blockage and method of blocking against the air differ according to the apparatus because the composition and property of the reagent used and the use environment are different. In some cases, it is necessary to attach a lid to a reagent container to block the air more. When the lid is attached, because the nozzle and the lid contact with each other, erroneous detection may occur in the liquid level detection by the capacitance method. Therefore, a mechanism for opening and closing the lid is required separately. Since it is also forced to add a new drive mechanism for opening and closing the lid, defects such as significant increase of the cost, enlargement of the apparatus size, and increase of the noise generated are thereby developed.
As an improvement plan therefor, there is a method in which the lid is made of an electro-conductive elastic body, and the liquid level is detected after the nozzle penetrates the lid. However, in aspirating the reagent, the reagent attached to the nozzle is attached to the lid also. In aspirating the reagent again, the reagent having been attached to the lid before is attached up to the root of the nozzle. Thus, increase of cross-contamination between the reagents (separate reagents are mixed to each other) is worried about. In order to solve the problem, it is necessary to clean the nozzle from the root in cleaning the nozzle.
In cleaning the nozzle, pure water is commonly used. When the quantity of the pure water used increases, the capacity of the pure water set to the apparatus increases; the capacity of a container for storing a waste liquid also increases by that rate, and the apparatus size increases. Also, there is a defect that, because cleaning is executed from the root, the volume of the pure water attached to the nozzle increases, and the reagent is diluted by the pure water attached to the nozzle in aspirating the reagent.